I try and help so the fish don't die. I suppose I could be a dick about it and not say anything and let the fish die to "teach him a lesson," but I don't think that's a very intelligent thing to do. Getting on your high horse and deciding to punish someone for not doing what you think they should do is more of the /b/ way of handling things.
The right thing to do is try and help him keep these fish alive and try to change his mind about things so that it doesn't happen again. Not helping is a good way to kill off these fish, a couple more batches, and potentially lose someone from the hobby. If you can get through to him and change his thinking you can wind up with another informed aquarist who will help spread the hobby rather than bad mouth it later. Do nothing and its guaranteed to turn out bad, do something and it could still turn out bad, but it might come out good. I'll take a 50/50 shot at making things better than a sure way to make it worse.